The radio frequency induction heating device of the Present invention has many and varied applications. For example, it could be used to heat treat a narrow portion of a machine tool, such as a cutter or the like, to harden that portion of the tool.
Co-pending application Ser. No. 06/439,909, filed Nov. 8, 1982 in the names of Jerry W. Schoen and Russel L. Young, and entitled LOCAL ANNEALING TREATMENT FOR CUBE-ON-EDGE GRAIN ORIENTED SILICON STEEL, teaches a local annealing treatment for both regular and high-permeability cube-on-edge grain electrical steels to improve the core loss thereof. According to this co-pending application, at some point in the routing of such electrical steels, after at least one stage of cold rolling and before the final high temperature anneal during which secondary grain growth occurs, the electrical steel is subjected to local annealing across its rolling direction, resulting in bands of enlarged primary grains. The bands of enlarged primary grains regulate the growth of the secondary cube-on-edge grains in the intermediate unannealed areas of the electrical steel strip during the final high temperature anneal. The enlarged primary grains of the annealed bands are, themselves, ultimately consumed by the secondary grains resulting in a cube-on-edge grain oriented electrical steel with smaller secondary grains and reduced core loss.
Co-pending application Ser. No. 06/439,884, filed Nov. 8, 1982 in the names of Jerry W. Schoen and Russel L. Young, and entitled LOCAL HEAT TREATMENT OF ELECTRICAL STEEL, discloses a process for improving the core loss of magnetic material of the type having a plurality of magnetic domains of such size that refinement thereof would produce significant core loss improvement. The magnetic material (such as cube-on-edge regular grain oriented silicon steel strip, cube-on-edge high-permeability grain oriented silicon steel strip and cube-on-face silicon steel strip) is subjected to a local heat treatment to produce parallel bands of heat treated regions extending substantially transverse the rolling direction of the magnetic material, with regions of untreated areas therebetween. The heat treatment alters the microstructure within the locally heat treated bands or regions, thereby regulating the size of the magnetic domains. The local heat treatment step is followed by an anneal resulting in improved core loss of the magnetic material. In an exemplary application to regular grain oriented silicon steel or high-permeability grain oriented silicon steel, the finished and finally annealed electrical steel, having a mill glass, an applied insulative coating, or both thereon, is subjected to local heat treatment wherein the heat treated bands are brought to a temperature above about 800.degree. C. in less than 0.5 seconds (and preferably in less than 0.15 seconds). The locally heat treated strip is then annealed at a temperature of from 800.degree. C. to about 1150.degree. C. for a time of less than two hours. The improved core loss is permanent and is achieved without damage to the mill glass or applied insulative coating.
The radio frequency induction heater of the present invention can be used in the practice of the teachings of both of the above mentioned co-pending applications and their teachings are incorporated herein by reference. While the induction heater of the present invention can be used to perform any appropriate heat treatment or annealing step, for purposes of an exemplary showing it will be described in its application to locally annealing a silicon steel strip during the routing thereof as taught in the first mentioned co-pending application and in its application as a device to locally heat treat fully developed cube-on-edge or cube-on-face silicon steels, as taught in the second of the above mentioned co-pending applications. Therefore, when used herein and in the claims, terms such as "locally heating" should be construed broadly enough to cover both a local anneal and a local heat treatment.
The radio frequency induction heating device of the present invention is especially suitable for local annealing or heat treating in high speed commercial applications, owing to the nature of the high frequency currents, the high power output available and the electrical efficiency. The induction heater is simple in construction, having a lower first cost than many other heating systems. It is more energy efficient, potentially safer and easier to maintain than other heating systems, such as laser systems or the like.